This invention relates to radio frequency pulse generating device and, in particular, to a light activated solid state generator capable of providing pulse bursts at microwave frequencies.
The prior art abounds with various methods for generating pulses of power at microwave frequencies. A particular family of microwave pulse generators utilize liquid or gaseous dielectric spark gaps to perform the relatively fast switching function. One technique utilizes these switches in a circuit arrangement commonly known as a frozen wave generator. This type of generator was capable of providing intense radio frequency pulses for plasma heating at frequencies having an upper limit approaching 1 MHz and later was improved to have an upper frequency limit approaching 200 MHz. However, since this technique requires simultaneous switching of a plurality of spark gaps, it has been plagued with problems of seemingly irreducible jitter inherently associated with spark gap switches. On the other hand, semiconductors, which are generally capable of jitter-free operation, are generally limited to operation at relatively low power levels because of the manner in which mobile charges are injected and depleted within the material.
The photoconducting properties of semiconducting materials are well known in the art; however, the development of a quasi-metallic photoconducting state in materials such as silicon has been demonstrated only recently. Lasers delivering microjoule-level pulses to areas of about 1mm.sup.2 have been known to produce quasi-metallic photoconduction in silicon with a corresponding change in conductance from 10.sup.-4 (ohm-cm).sup.-1 to 10.sup.3 (ohm-cm).sup.31 1. The switching of the silicon is limited only by the optical pulse since the dielectric relaxation time is less than 1 psec. Electrical voltages, 100 volts and higher, are capable of being switched in this manner. In U.S. Pat. No. 3,917,943 to D. H. Auston, there is disclosed a means for obtaining pulse widths of 15 psec at power levels in the order of 100 watts. Also known in the art are light-activated multilayer silicon devices that provide nanosecond-risetime switching with multimegawatts of peak power. A typical light activated solid state switching device is disclosed in U.S. Pat. No. 3,893,153 to Derrick J. Page and John S. Roberts issued July 1, 1975.
The present invention overcomes the shortcomings of the prior art relating to frozen wave generators by utilizing solid state switches which makes use of the injection of charge by photon absorption. The photon absorption phenomenon is only limited by the speed of the light pulse risetime. As a result, fast switching may be obtained at potentials up to those required for the electrical breakdown of the bulk material.
Therefore, it is an object of the present invention to provide a light activated switching generator capable of providing jitter-free pulses at microwave frequencies.
It is a further object of the present invention to provide a light activated solid state microwave generator capable of providing jitter-free pulses at microwave frequencies.
Another object of the present invention is to provide an array of solid state optoelectronic switches capable of generating bursts of radio frequency pulses from a DC input voltage source.
A further object of the present invention is to provide a solid state switching generator for generating microwave power at higher power levels than known heretofore.
Still another object of the present invention is to provide a solid state switching microwave generator capable of providing pulses at higher frequencies than known heretofore.
Yet another object of the present invention is to provide an optoelectronic solid state circuit arrangement capable of generating a frozen wave at microwave frequencies.
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part thereof, and in which is shown by way of illustration a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the invention is best defined by the appended claims.